Hi i am Dr Ahmed Aly thanks for using HealthcareMagic site , I had gone through your question and understand your concerns .. I hope you feel better soon , i think it could be a muscular sprain or spasm . rarely it could be sciatica due to nerve compression but i do not think this could have happened to you as you seem a physically active person ( pilates ) You are doing fine by your physical stretching , straightening exercises and even yoga as it is the first line of treatment for sciatica . try to avoid heavy lifting , over weighing , vigorous movements , bad sleeping or sitting postures . I think you shall warm up a little bit before your classes to decrease the chances of muscular spasms , you could use pain killers like advil tabs when needed , hot massages with topical anti-inflammatory gels , B12 vitamin supplementation and muscle relaxants will be more than enough for your cases . If pain persists i recommend X rays and MRI scan to exclude any spinal injury and follow them up with your physician for proper evaluation and management . Please click and consider a 5 star rating with some positive feedback if the information was helpful. Wish you good health, Any further clarifications feel free to ask.